In automated assembly systems devices are used for holding and placing components or parts to accomplish the manufacture of finished or intermediate products. These automated assembly systems ideally employ as much robotic operation as possible in order to minimize or eliminate the need for manual intervention. Parts or components in such systems are typically acquired by the robot in one of two ways. The first way is to use an end effector which acquires a particular part by vacuum acquisition wherein a bellows or open ended tube engages a surface of the part and the vacuum is drawn through the bellows or tube to thereby hold the part to the bellows or the open ended tube. An example of an open ended tube device is shown in U.S. Pat. No. 5,308,132 to Kirby et al. An example of a bellows arrangement is shown in U.S. Pat. No. 4,662,668 to Hufford. It is important that when a robot attempts to acquire a part, that the robotic controller receive the signal that the part has either successfully been acquired or not been acquired. In the case of the Hufford device, a proximity sensor is located within the vacuum cup.
U.S. Pat. No. 5,207,467 to Smith teaches a vacuum pick-up device which employs a visual indicator for determining the present or absence of a component on the end of the vacuum pick-up device. A monitor is provided which has a transparent body portion and air flow passages therethrough. An indicator is provided for each vacuum pick-up device and is contained within the air flow passageway for that particular vacuum pick-up device. The position of the indicators within the flow passages is dependent upon the presence or absence of a component on the end of the vacuum pick-up device.
U.S. Pat. No. 5,102,114 to Suda teaches a vacuum pick-up type device wherein suction cups are used to engage sheets of glass. A pressure switch is electrically connected to the robot to supply electrical signals representative of attachment and detachment of the suction cup to the glass. The pressure switch which is a form of pressure sensor is provided in the vacuum supply line to the suction cup. The pressure switch is switched on when the pressure in the supply line is lower than a predetermined value and switched off when the pressure in the supply line is higher than a predetermined value.
U.S. Pat. No. 5,064,234 to Marozsan et al teaches a vacuum pick-up device for use in automated and/or robotic assembly specifically for use in securing electrically conductive components. The device employs an electric conducted sensor for detected the presence of the electrically conductive component at the vacuum nozzle.
U.S. Pat. No. 4,657,470 to Clarke et al teaches a robotic end effector which includes a vacuum-operated quill for picking up integrated circuits. The end effector includes a tactile sensor. This sensor permits sensing of contact between either the integrated circuits being positioned and the adhesive layer on the circuit board or contact between the integrated circuit and the circuit board.
The second principal way in which robotic arms acquire parts or components is through gripping action. Typically, a pair of fingers are operated by a robot such that they are movable toward and away from each other such that the fingers can be manipulated to hold a component therebetween. This type of arrangement is taught in U.S. Pat. No. 5,671,962 to Otsuka et al. The Otsuka device employs a work-detector sensor attached to one of the pair of fingers. The robot controller receives a signal from the work-detector sensor to indicate whether or not a work piece exists between the fingers.
In robotic operations it is often necessary to change end effectors for acquisition of different types of components and, particularly, to change the type of parts acquisition tool being used. That is, in one operation the robot may be employing a vacuum acquisition end effector. In another operation the robot may need to employ a finger gripping-type tool. The prior art fails to teach an end effector system which can be used to both acquire parts by vacuum and by finger gripping.